Published German patent document DE 102 21 376 describes a method and a device for controlling an internal combustion engine. It describes a method and a device for controlling an internal combustion engine in which a lambda value of the exhaust gas is determined on the basis of performance characteristics. This value is compared to the actual lambda value, and this comparison is used to calculate a correction value for correcting a fuel amount signal or an air amount signal.
Essentially, a first quantity characterizing the actually injected fuel amount is determined from the sensor signal of a lambda sensor and an air mass sensor and compared to a second quantity characterizing the desired fuel amount to be injected. A first correction value for correcting a fuel amount and/or a second correction value for correcting an air amount is defined based on this comparison.
In an ideal, error-free system, the actually injected fuel amount must be equal to the desired fuel amount. Due to tolerances and/or aging effects, the desired fuel amount differs from the actually injected fuel amount. If the air amount metered to the engine is controlled and/or regulated as a function of the desired fuel amount to be injected, an erroneous air amount is set. Control as a function of the actually injected fuel amount is not able to be easily accomplished, because the actually injected fuel amount is difficult to determine. By measuring the lambda value of the exhaust gas and the air amount metered to the engine, the actually injected fuel amount may be computed and compared to the desired fuel amount to be injected. The difference between these two signals provides a correction value. This correction value may be used to influence the air system. This is accomplished, for example, by correcting the fuel amount value supplied to the air system using the appropriate correction value. Furthermore, the air amount may be directly corrected as appropriate. As an alternative to computing the fuel amount, the lambda signals or other quantities characterizing the fuel amount may also be used directly.
Alternatively, the fuel metering system may be influenced directly in such a way that a fuel amount quantity is corrected using the correction value until the fuel amounts to be injected and actually injected are the same. The problem with such a direct correction of the fuel amount is that such a correction may result in an increase in the amount of fuel. Therefore, for safety reasons, it is not desirable for direct intervention in the fuel amount to correct differences of any magnitude or for it to act in the entire range of engine operation.
These limitations do not apply in the case of indirect intervention, for example, via air control using exhaust gas recirculation. Because indirect intervention is at least equivalent or better in terms of emissions, indirect intervention in the air amount is preferred.